In conventional elevator apparatuses, a car buffer and a counterweight buffer are installed in a hoistway lowermost portion. These buffers have a role of braking and stopping a hoisted body (a car or a counterweight) when the hoisted body could not be braked and stopped before the hoistway lowermost portion by braking apparatuses and safety devices. If we let d be the average deceleration during braking by these buffers, Vc be the speed when the hoisted body collides with a buffer, and t be the deceleration time, then braking distance L is expressed by the following expression:L=(1/2)d×t2  (1)
Now, from Vc−d×t=0, we can assume that the deceleration time t is t=Vc/d to obtain the following expression:L=(1/2)d×t2=(1/2)d×(Vc/d)2=Vc2/2d  (2)
An upper limit is prescribed for the average deceleration d in order to suppress mechanical shock to which the passengers inside the car are subjected during braking and stopping. For this reason, it is necessary to lengthen the braking distance L as the speed Vc at which the hoisted body collides with the buffer increases, and it is necessary to ensure a buffer stroke that is greater than or equal to this braking distance.
In the European Standards (ENs) (EN 81-1:1998 (10.4.3.1)), for example, a buffer stroke that is sufficient to brake and stop a car is required under conditions in which the buffer impact speed Vc (m/s) is 115 percent of the rated speed Vr (m/s), and the upper limit of the average deceleration d (m/s2) is gravitational acceleration g (=9.81 m/s2). Consequently, from Expression (2), the buffer stroke Lst (m) is given by the following expression:
                                                                        Lst                ≥                L                            =                            ⁢                                                                    Vc                    2                                    /                  2                                ⁢                                                                  ⁢                g                                                                                        =                            ⁢                                                (                                                            1.15                      2                                        ×                                          Vr                      2                                                        )                                /                                  (                                      2                    ×                    9.81                                    )                                                                                                        ≅                            ⁢                              0.0674                ⁢                                                                  ⁢                                                      Vr                    2                                    ⁡                                      (                    m                    )                                                                                                          (        3        )            
A buffer stroke is also prescribed in Japanese building standards laws with similar aims to the ENs.
Now, in conventional mechanical governors, if car speed reaches a first excessive speed detection level (Vos), an overspeed switch is operated such that passage of electric current to a hoisting machine motor is interrupted and a braking apparatus is activated to brake. Rotation of a driving sheave is thereby braked and stopped, making the car perform an emergency stop. If the car speed reaches a second excessive speed detection level (Vtr) that is higher than the first excessive speed detection level, a speed governor rope is gripped to activate a safety device. A braking force is thereby applied directly to the car to make the car perform an emergency stop.
In mechanical governors of this kind, since the overspeed switch is operated, and the speed governor rope is gripped, etc., using a centrifugal force that is generated in proportion to the square of the car speed, the excessive speed detection levels (Vos and Vtr) are constant throughout the hoistway. Because of that, the excessive speed detection levels (Vos and Vtr) are set to levels that exceed the rated speed Vr even in upper and lower terminal portions of the hoistway where the car decelerates during normal running. Consequently, it has been necessary to design the buffer stroke such that “the buffer impact speed is a speed that is higher than the rated speed, and increases as the rated speed increases.”
The buffer strokes found using Expression (3) for cases in which the rated speed is 5 m/s (300 m/min) and 10 m/s (600 m/min), for example, are 1.685 m (for the rated speed 5 m/s) and 6.74 m (for the rated speed 10 m/s), respectively.
In high-speed elevator apparatuses, enlargement of the buffer strokes becomes particularly pronounced as the rated speed increases, and the accompanying increases in hoistway space have been problematic.
Conventionally, emergency terminal speed limiting devices have been considered as a method for solving these problems. In emergency terminal speed limiting devices, an excessive speed detection level (Vets) that becomes progressively lower is set in hoistway terminal portions in which a car decelerates during normal running. An anomalous car speed in the hoistway terminal portions early can thereby be detected to enable the buffer stroke to be shortened by reducing buffer impact speed.
In recent years, techniques have also been proposed in which excessive speed detection levels (Vets) are lowered continuously (steplessly) (see Patent Literature 1, for example).
However, in conventional emergency terminal speed limiting devices such as that described above, because the car is made to perform an emergency stop using a braking apparatus when an anomalous speed is detected, in the rare event that the main ropes suspending the car and the counterweight all break, the braking force from the braking apparatus does not act on the car, and the car is not decelerated until the car speed reaches the second excessive speed detection level (Vtr) in the mechanical governor and safety devices are activated.
Because of that, even if conventional emergency terminal speed limiting devices are used to shorten the buffer stroke, the amount of reduction compared to standard buffer strokes is limited, and there is also no change in the relationship that the buffer stroke is lengthened as the rated speed increases.
In European Standard EN 81-1:1998, for example, it is recognized that the buffer stroke is shortened by up to ⅓ of the standard stroke when an emergency terminal speed limiting device is applied to a high-speed elevator that has a rated speed in excess of 4 m/s. In other words, as shown in Expression (3), the standard buffer stroke is 0.0674 Vr2, but when an emergency terminal speed limiting device is used, the buffer stroke becomes 0.0674 Vr2/3 or greater.
Regarding problems such as breakage of the main ropes, countermeasure techniques have been proposed such as stopping operation of the elevator apparatus when even a single main rope breaks. In addition, techniques have also been proposed in which safety devices are activated upon detecting breakage of a main rope (see Patent Literature 2, for example).